Dave Lucia, a well known person in the Elixir community of practice, posted this tweet:

Friends who do contract work:
How do you track your hours?
Do you have a minimum time slice that you track by?
How do you keep track of tasks that you’re billing?
This is all new to me, and using a Notion table feels a bit cumbersome
All tips appreciated 🙏

There are several interesting answers there:

• "If it's just you, pencil and paper. Seriously. And whenever it's billed throw it away. Keep it simple without adding cumbersome tools. Buy a nice pencil."
• "Longtime Freshbooks user here. Does everything I need without getting in the way."
• "I use timingapp.com"
• "For me tracking anything in increments less than an hour is a nightmare. I’m TERRIBLE at tracking time though. I’ve used many tools for it (mostly Toggl) but they’re all so similar. I’ve always wanted to try a physical device like Timeular."
• "I had a Google sheet that I logged everything into (daily hours) and then invoiced every 2 weeks. Not too tricky that way!"
• And more. Some people suggested using Harvest.

As I do not work as a contractor, I decided to ask "ChatGPT Mar 23 Version" (which says that it is a "Free Research Preview" and that "ChatGPT may produce inaccurate information about people, places, or facts.") the same questions. My prompt was:

I have a few questions about contract work in software development.
How do developers track their hours?
Do they have a minimum time slice that they track by?
How do they keep track of tasks that they are billing?

ChatGPT's answer was:

Developers who work on a contract basis typically track their hours using time tracking software or tools. There are many different time tracking tools available, including Toggl, Harvest, RescueTime, and many others. These tools typically allow developers to track the time they spend on specific tasks or projects, and can generate detailed reports that can be used for invoicing clients.

In terms of minimum time slices, this can vary depending on the developer and the client. Some developers may track their time in 15-minute or 30-minute increments, while others may track their time in smaller or larger increments. The minimum time slice that a developer tracks by will typically be determined by the client's requirements and any contractual agreements that are in place.

To keep track of tasks that they are billing, developers may use project management software or tools. These tools can help developers organize their work, track their progress, and ensure that they are completing tasks on time and within budget. Project management tools can also be used to generate invoices and track payments, making it easier for developers to manage their finances and ensure that they are being paid for their work.